Heterodimeric Plasmonic Nanogaps for Biosensing

Abstract

We report the study of heterodimeric plasmonic nanogaps created between gold nanostar (AuNS) tips and gold nanospheres. The selective binding is realized by properly functionalizing the two nanostructures; in particular, the hot electrons injected at the nanostar tips trigger a regio-specific chemical link with the functionalized nanospheres. AuNSs were synthesized in a simple, one-step, surfactant-free, high-yield wet-chemistry method. The high aspect ratio of the sharp nanostar tip collects and concentrates intense electromagnetic fields in ultrasmall surfaces with small curvature radius. The extremities of these surface tips become plasmonic hot spots, allowing significant intensity enhancement of local fields and hot-electron injection. Electron energy-loss spectroscopy (EELS) was performed to spatially map local plasmonic modes of the nanostar. The presence of different kinds of modes at different position of these nanostars makes them one of the most efficient, unique, and smart plasmonic antennas. These modes are harnessed to mediate the formation of heterodimers (nanostar-nanosphere) through hot-electron-induced chemical modification of the tip. For an AuNS-nanosphere heterodimeric gap, the intensity enhancement factor in the hot-spot region was determined to be 106, which is an order of magnitude greater than the single nanostar tip. The intense local electric field within the nanogap results in ultra-high sensitivity for the presence of bioanalytes captured in that region. In case of a single BSA molecule (66.5 KDa), the sensitivity was evaluated to be about 1940 nm/RIU for a single AuNS, but was 5800 nm/RIU for the AuNS-nanosphere heterodimer. This indicates that this heterodimeric nanostructure can be used as an ultrasensitive plasmonic biosensor to detect single protein molecules or nucleic acid fragments of lower molecular weight with high specificity.

Manipulating acoustic and plasmonic modes in gold nanostars

“…Gold nanostars are synthesized using one-step (without seed) surfactant-free wet chemistry method as described elsewhere. [59] The method is briefly written in the experimental section. Figure 1 nm core, support that the LSPR is expected at 1060 nm (1.17 eV) and thereby confirm the dipolar (bright) edge mode nature at the pinnacle (see Figure S3).…”

“…Gold nanostars are synthesized using one-step (without seed) surfactant-free wet chemistry method as described elsewhere. [59] The method is briefly written in the experimental section. Figure 1(a) shows a typical higher magnification TEM image of a gold nanoparticle while Figure 1(b) shows a lower magnification TEM image where almost all the nanoparticles have at least one spike in their surface, confirming the relatively high yield of the synthesis method.…”

“…Here, for our study we have synthesized these highly tunable, stable, efficient AuNSs using a low-cost, simple, one-step (seedless), surfactant-free, high-yield wet chemistry method. [59] In this contribution we report experimental evidence of both the plasmonic edge modes and breathing acoustic modes in AuNS. Results from optical and electron spectroscopy characterization of these highly stable nanoparticles (stability>5 months in aqueous solution) are reported.…”

“…Here, for our study we have synthesized these highly tunable, stable, efficient AuNSs using a low-cost, simple, one-step (seedless), surfactant-free, high-yield wet chemistry method. 59 …”

Engineered Gold-Based Nanomaterials: Morphologies and Functionalities in Biomedical Applications. A Mini Review

“…( a , b ) AuNSs TEM images, reproduced and adapted with permission from [161,162] respectively. ( c , d ) AuNCs TEM images adapted with permission from [74].…”